1. Field of the Invention
This disclosure relates to the field of chemical purification. In particular, to the field of purifying 5-sulfoisophthalic acid by use of an acetic acid wash.
2. Description of the Related Art
5-sulfoisophthalic acid is a molecule which can be used in treating nylon-based textiles with the purpose of achieving stain resistance due to the ability of the 5-sulfoisophthalic acid to act as a topical “stain blocker” by associating with, and thereby blocking access to, acid dye sites or for other uses known to those of ordinary skill in the art. In order to obtain 5-sulfoisophthalic acid, traditionally the sulfonation of isophthalic acid using 30% oleum is performed. This produces a mixture which includes impurities. To remove the impurities solvents have been used to wash the 5-sulfoisophthalic acid.
There are a number of common problems inherent to the solvents which have been used in this process which include the following. First, solvents such as water and acetone are known to dissolve a significant quantity of the product as they are removing impurities. This decreases the resultant yield of product from each production run or batch. Other solvents, such as methanol, react with the product to produce undesired esters. Still further solvents, such as toluene and heptane, do not displace the primary impurities of the solution. Thus, the generally used solvents and purification processes currently employed in the art are either ineffective or require large quantities of the solvent to remove the impurities, additional equipment, excess labor, and increased cycle time; all while resulting in a lowered yield of the final product.
Czech Patent CS 157260 19750415, indicates in its abstract that sulfonated aromatic carboxylic acids (including 5-HSIPA) can be purified by being digested with an acetic acid which removes sulfonic acids, carboxylic acids and residual acid. Digesting (re-slurrying or re-pulping) generally involves the complete isolation of the crude product, re-introduction into a digesting unit with enough solvent to allow adequate agitation, a hold time, and a re-isolation of the product. While this disclosure is a step forward from the conventional solvents and purification processes previously discussed because it can produce increased yield, there are still numerous problems. For example, the crude product still needs to be isolated in this process, a large quantity of acetic acid is still needed to displace the impurities, and additional labor, equipment, and time are required, resulting in increased production costs.